Wire coil winding apparatus and method

ABSTRACT

Apparatus and method is provided for converting a long indefinite length of wire from a supply bundle into a measured length, tightly wound coil. The wire is driven from the supply by a constant speed capstan to a winding station. A measured length of wire is wrapped around a mandrel between a pair of flanges under controlled tension conditions. After winding, a series of bands are passed through the coil bore and respective ends of banding material are twisted together and flattened against the coil surface. The banded coil is ejected from the mandrel to a conveyor or container.

[0001] This Invention is a Divisional of patent application Ser. No. 10/234,752, filed Sep. 4, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of wire coil winding and more particularly to apparatus and method for winding a wire coil and automatically banding the wound coil.

BACKGROUND OF THE INVENTION

[0003] Wire is generally supplied in one of three types of package, cut straight lengths in a box, wound on a spool or reel, and wound into a coil without any supporting spool. The present invention involves winding wire into a coil without any spool. Most wire, although somewhat susceptible to retaining a shape into which it is bent, will also exhibit a degree of resiliency and tend to partly return to its pre-bend shape. Therefore, a wire that has been wound into a coil shape will naturally tend to partly straighten, or expand diameterally. In addition, wire is normally wound in coils by the technique known as parallel winding, rather than cross winding. Parallel winding has no significant transverse vector to prevent the wound coil from spreading axially and losing its shape integrity.

[0004] Both the diameteral expansion and the axial spread have been historically controlled with banding that was applied by an operator manually placing a wire or tape through the center and around the periphery of the coil. If the banding material is a wire, the operator performing the banding operation twisted the ends together, trimmed the excess banding and flattened the twisted wire against the coil periphery. If the banding material is tape, coil security may require multiple wraps for each position. Since a typical wire coil needs three or four circumferentially separated bands for secure support, this manual operation involves a significant amount of time and effort. The time involved both prevents the machine devoted to coil winding from further production during the banding operation and increases the labor cost of making the wire coil.

[0005] Therefore, it is an object of the present invention to provide a wire coiling apparatus and method capable of automatically banding a wound coil.

[0006] It is an additional object of the present invention to provide a wire coiling apparatus and method capable of automatically banding a wound coil with a wire band and causing the twisted ends of banding wire to be flattened against the coil.

[0007] These and other objects will become more apparent from the description of the invention to follow.

SUMMARY OF THE INVENTION

[0008] A wire coil winding machine is provided with an automatic coil banding mechanism. The wire is wound on a mandrel between a pair of flanges to form a coil. The mandrel and flanges as a unit have a number of channels cut into their mutual inner surface. At the completion of winding a selected quantity of wire, the winding stops. A series of bands are automatically driven through a channel so as to encircle the coil from its bore to its circumference. The ends of the bands are secured around the coil. The completed coil is ejected from the mandrel and a second coil is started.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a schematic elevation view of the coil winding apparatus of the present invention.

[0010] FIGS. 2A-2D are a series of detailed sequential operational diagrams of a coil banding section of the apparatus of the present invention.

[0011]FIG. 3 is an enlarged cross sectional view of the coil winding mandrel and flanges as taken in the direction of line 3-3 of FIG. 2A with a completed wire coil mounted thereon.

[0012]FIG. 4 is an enlarged perspective view of a wound and banded wire coil as formed according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] According to the illustration of FIG. 1, the present invention provides a machine 10 for winding a wire supplied in long continuous lengths into compact, uniform coils. Although the preferred embodiment of the invention is depicted in terms of winding a wire product, i.e. an elongate metallic member, it is recognized that the principles of the present invention can be applied to other bendable materials, such as monofilament plastic materials. A loosely formed wire supply bundle 14, formed of a long length of wire 18, is mounted onto a wire supply holder 12 at the entry end of coiling machine 10. For satisfactory operation, wire supply bundle 14 must be formed with the wire in substantially parallel, not tangled, loops. The present invention also contemplates winding wire from a supply spool to a coil. The possible supply spool may optionally be allowed to revolve around a shaft with an applied drag or remain still while the wire is pulled off axially, perhaps with the aid of a flyer, as is known. The wire 18 is threaded from supply holder 12 through a guide 20 that is situated over the approximate center of supply holder 12, and then past a break-out sensor 22 to be wrapped partly around pulley 24. Wire 18 is held in intimate contact with the surface of pulley 24 by a captured belt (not shown) which is in contact with a portion of the circumference of pulley 24. Wire 18 travels in the direction indicated by several arrows along its length. Sensor 22 may be any sort of known sensing device to confirm the presence of wire 18 adjacent thereto, or, if no wire 18 is detected, to stop operation of apparatus 10 or signal an operator that a problem exists. The entry edge of pulley 24 is vertically aligned with guide 20 and sensor 22. Pulley 24 is rotatably mounted on a shaft and is able to create an adjustable amount of running tension in wire 18 by the application of a controllable drag, for example as created by a magnetic brake 26. Alternate means for creating tension, for example a mechanical brake, would also perform the basic function required. However, the use of magnetic brake 26 permits adjustment and control of its applied drag with electrical signal input from a microprocessor such as PLC 68, according to the preferred embodiment of the invention.

[0014] Wire 18 is then threaded in an elongated loop around a dancer assembly including rotatably mounted sheave 30 and dancer sheave 32 to pass through guide 38 and wound partly around drive capstan 40. Sheave 30 and dancer sheave 32 each represent multiple sheaves on a pair of common shafts, in the preferred embodiment. Sheave 30 is mounted fixedly in a position so its top edge is preferably in tangential contact with a horizontal line extending from the top of tension pulley 24 to the center of guide 38. Dancer sheave 32 is mounted so as to be able to move, e.g. upwardly, in response to increased tension on wire 18 in the direction indicated by arrow A. When wire 18 is running without tangles in the range of normally applied supply tension, dancer sheave 32 is in its normal state being held at or close to the bottom of its travel distance by an applied force, in the preferred embodiment being caused by a pneumatic cylinder (not shown). A detector 34 is positioned adjacent dancer 32 to provide a warning signal or to shut down machine 10 in case of a great increase in operating tension on wire 18. For example if supply bundle 14 becomes tangled or wire 18 is snagged, dancer sheave 32 will be raised, due to the tension on wire 18, to the position shown in dashed lines 32 a, and detector 34 will be actuated.

[0015] Continuing with reference to FIG. 1, after passing through guide 38, wire 18 is wrapped partly around drive capstan 40 which is driven by a motor (not shown). Wire 18 is held in intimate contact with drive capstan 40 by means of a captured belt (not shown) which conforms to drive capstan 40 around approximately one quarter of its circumference. Alternately, wire 18 may be wrapped multiple times around drive capstan 40 for secure drive speed control. Capstan 40 operates at a substantially constant rotational speed to impart the force to drive wire 18 at a substantially constant linear speed. A guide tube 42 is mounted along a line that is vertically tangent to the exit edge of drive capstan 40 and perpendicularly centered on an upper surface of cutter 46. Guide tube 42, in the preferred embodiment, is formed with two partial tubes that are telescopically extendable in the direction indicated by arrow B. The upper portion of guide tube 42 is vertically positionable as shown by arrow B to be close to capstan 40 during operation of apparatus 10 and farther from capstan 40 for ease of threading wire 18 therethrough. A device, e.g. a locking collar (not shown), is provided to affix guide tube 42 at a selected length. The lower end of guide tube 42 is fixedly mounted an arbitrary distance above cutter 46.

[0016] Cutter 46 is formed, in the preferred embodiment, by an upper and a lower guide plate, each having a vertical through hole formed therein. Each through hole is aligned with the other through hole during winding of a wire coil in machine 10 to allow wire 18 to pass freely. Alternate cutter designs may be employed within the scope of the present invention. Wire 18 is moved by capstan 40 to pass through telescoping guide tube 42 and through the aligned upper and lower holes in cutter 46. The forward end of wire 18 ultimately moves to a winding station to pass in contact with guide pulley 48 that is positioned beneath and aligned with the guide holes in cutter 46. In the preferred embodiment, the leading end of wire 18 is fed past guide pulley 48 and into a hole or slot in mandrel 72 at the beginning of a winding cycle. Coil winding proceeds at a relatively slow rotational speed for several revolutions, e.g. four revolutions, until wire 18 is securely engaged on mandrel 72, and then gradually accelerates to a pre-selected constant linear running speed which is maintained for the balance of the wind cycle. The running speed of wire 18 is preferably a substantially fixed linear speed as controlled by drive capstan 40. The rotation of coil 50 is driven at decreasing rotational speed by a motor (not shown) that is operating in what has been known as torque mode so as to match the fixed linear speed of and provide drawing tension to wire 18.

[0017] Guide pulley 48 is maintained in a fixed position to control wire 18 as it is wound into a coil 50 as described more fully below. During the winding cycle in which coil 50 is formed, coil 50 is rotated in the direction indicated by arrow C, and coil 50 is simultaneously moved axially in a direction into and out of the plane of FIG. 1 to create a slow traverse parallel-wound coil. “Parallel wound” is a term used to indicate that each loop of wire 18 in coil 50 is substantially perpendicular to the axis of coil 50 and substantially parallel to other wire loops in a wire layer. The pitch of winding from a first to a subsequent adjacent wire loop on the circumference of coil 50 is adjustable by changing the speed at which coil 50 is caused to traverse (into and out of the plane of FIG. 1) while the linear speed of wire 18 remains constant so as to optimize productivity. The traverse movement of coil 50 is driven by a separate drive motor connected to a linear actuator, for example a drive screw mechanism.

[0018] Coil 50 is wound in the winding station on a mandrel 72 between two spaced apart flanges as will be described more fully below. Mandrel 72 is rotated by a motor capable of variable speed operation and having an encoder to signal the number of revolutions run and its angular position. Coil 50 winding continues to rotate until a pre-set value, representing a selected length of wire 18, has been reached. A finished coil 50 is preferably similar in outer diameter to the diameter of flanges 70 a and 70 b. At the completion of the winding cycle, wire 18 and mandrel 72 gradually decelerate and simultaneously stop operating. A banding supply station 54 supplies plural lengths of banding material 56, preferably a banding wire, to place multiple bands perpendicularly from the bore to the periphery of coil 50. After the application of one or more bands, one of the guide plates of cutter 46 is caused to move, e.g. by a pneumatic cylinder, in a direction perpendicular to the linear direction of wire 18 to sever wire 18 in a scissor-like action between the upper and lower guide holes. The plates of cutter 46 are returned to their normal position in which the guide holes are aligned. Coil 50 is caused to rotate slowly for a portion of a revolution in a direction opposite to that indicated by arrow C to cause the cut end of wire 18 to engage bar 52 and be turned backwards as compared to the direction in which coil 50 was wound. In this manner, wire 18 is secured against unraveling by being locked around a band of banding wire 56. Mandrel 72 and coil 50 are indexed 900 to apply each successive band in the manner described above until a selected number, e.g. four, bands are applied.

[0019] FIGS. 2A-2D illustrate sequential operational steps of positioning coil 50 for banding, passing a banding material through the bore of coil 50, bringing the ends of the banding material together, and twisting the ends of banding material together. As illustrated in sequential FIGS. 2A-2D, coil 50 is banded by wire banding material 56, supplied by banding supply station 54 and banding driver and cutter mechanism 58. FIG. 2A is a vertical plan view of the winding mandrel 72/flange 70 a combination and separable flange 70 b with a coil 50 formed therebetween at the end of the winding cycle. Banding material 56 is moved from banding supply station 54 toward coil 50. Depending on the characteristics of banding wire 56, banding driver and cutter mechanism 58 is optionally equipped with a wire straightening unit, as is known. Wire banding material 56, for purposes of banding, is preferably relatively annealed, as opposed to being hard and resilient, so as to be compliant when twisted.

[0020] In FIG. 2A, flange 70 a is seen to have a series of channels 76 that are separated circumferentially at angles of 90° from one another. As seen in FIGS. 2 and 3, channel 76 is wider at the periphery of flange 70 a than it is in the portion cut into mandrel 72 and in the continued narrow channel passing outwardly radially along flange 70 b. Channels 76 are open toward the inner surfaces of flanges 70 a, 70 b and mandrel 72. The mouth of channel 76 a is relatively wide both in the circumferential and the axial direction of flange 70 a. Flange 70 b is separable from mandrel 72 (see FIG. 3) by being moved in the direction indicated by arrow H.

[0021] Returning to FIG. 2A, banding wire 56 is moved from supply station 54 toward flange 70 a. Banding wire 56 is cut to a desired length by a cutting mechanism 58 as is known in the trade. An alternate possibility is to supply precut lengths of banding wire 56. In FIG. 2B, banding wire 56 passes through flange 70 a and through channel 76 to exit from flange 70 b. A pair of forks 74 a and 74 b, each formed with a “V” shaped open end that are oriented to face one another, are then caused to move toward each other in the direction indicated by arrows F to press the ends of banding wire 56 toward each other, forming a loop around one portion of coil 50. Once the ends of banding wire 56 are brought together, shown in FIG. 2C, jaws 62 a and 62 b are pivoted toward each other in the direction of arrows E, to clamp onto the ends of banding wire 56, and forks 74 a and 74 b are separated in the direction of arrows F to rest in the positions shown in FIG. 2D. In FIG. 2D, jaws 62 a and 62 b are shown as being caused to rotate in the direction shown by arrows G while maintaining pressure to grip the ends of banding wire 56 so as to twist the ends of banding wire 56 together. Jaws 62 a and 62 b may optionally be rotated either clockwise or counterclockwise. After a predetermined number of twists have been imparted to the ends of banding wire 56, e.g. 8-12 turns, jaws 62 a and 62 b separate. Jaws 62 a and 62 b are formed with a pressure contact area (not shown), and the number of turns applied by jaws 62 a, 62 b is determined to be sufficient to securely bind coil 50 and cause the portion of banding wire 56 distal from coil 50 to break off. Jaws 62 a and 62 b open, and coil 50 is rotated 900 to position another set of channels for the insertion and securing of banding wire 56.

[0022] The forming of wire bands as described above results in a twisted wire end protruding radially outwardly from coil 50 at each band position, i.e. four locations. In order to flatten the twisted wire ends against the peripheral surface of coil 50, bar 52 (see FIG. 1) is located close to the circumference of finished coil 50. Coil 50 rotates between sequential banding operations, causing the twisted ends of banding wire 56 to be bent toward the circumferential surface of coil 50. Lastly, ram 66 is advanced rapidly in the direction of arrow D to impact the twisted ends. Ram 66 is shaped substantially to match the contour of the periphery of coil 50. This flattening operation is repeated for each of the plural banding wires. Ram 66 is actuated by a pneumatic cylinder or other driver.

[0023]FIG. 3 provides an enlarged, detailed cross sectional view of flange 70 a mandrel 72 and flange 70 b with completed coil 50 in position therebetween. Flanges 70 a and 70 b surround coil 50, and banding wire 56 (shown as a dashed line) passing through channel 76 a proceeds across the mandrel portion to exit through flange 70 b. At the completion of winding and banding coil 50, flange 70 b separates from the fixed assembly of flange 70 a and mandrel 72, and an ejector (not shown) discharges coil 50 from mandrel 72 onto a receiving conveyor or into a container.

[0024]FIG. 4 illustrates coil 50 in completed wound and banded form with four bands 56 individually wrapped through the bore and around the periphery of coil 50. A typical set of dimensions for completed coil 50 is that bore diameter d equals about 4.1 cm (1.625 inch), outer diameter D equals about 13.6 cm (5.375 inch), and traverse width W equals about 4.6 cm (1.812 inch). Coil size is dependent upon the ultimate use to which coil 50 is put.

[0025] Coiling machine 10 (FIG. 1) is operationally controlled by microprocessor 68 connected thereto. Microprocessor 68 is capable of installing a previously recorded program or accepting operator-set parameters to automatically control the coil winding process of machine 10. Each parameter is represented by a counter and display on a screen (depicted as circles on the screen of microprocessor 68), with controls set to selected values by use of a touch screen or a keyboard. Relevant parameters, according to the preferred embodiment, include wire linear speed, mandrel traverse speed, wire diameter, number of mandrel 72 turns at slow speed before accelerating to running speed, magnetic brake 26 force to instill tension, mandrel 72 drive torque, total length of wire 18 on coil 50 before stopping winding, length of banding wire 56, number of banding wire 56 twists and number of ram 66 impacts per wire banding. Microprocessor 68 receives signals from sensor 22 as to the presence of wire 18 and from detector 34 as to the position of dancer 32 and of potentially excessive tension in wire 18, as well as operational information such as the linear running speed and quantity wound of wire 18 and the number of coils 50 completed in the production lot. Microprocessor 68 is adapted to save the operating parameters for a complete program in an internal memory or to record to a disc for future use. Alternately, the parameters comprising the operating program may be saved to a tape or disc memory device.

[0026] Therefore, the sequence of operations for automatic coil winding according to the preferred embodiment of the invention is as follows, referring to FIG. 1 for reference. An operator places a wire supply package 14 on wire supply holder and threads the wire 18 through guide 20, past wire presence sensor 22 and around pulley 24 with magnetic brake 26. Wire 18 is further threaded around sheave 30 and dancer sheave 32 which is monitored by detector 34 to signal the operator and/or shut down operations in the event of excessive tension. Wire 18 next passes through guide 38 and around drive capstan 40, through telescopic tube 42, through cutter plates 46 and around pulley 48 to mandrel 72. The operator either manually enters values for winding control on microprocessor 68 or inputs a pre-recorded control program. Wire 18 is fed into a slot in mandrel 72, and mandrel 72 slowly rotates as it slowly traverses axially. At the completion of several rotations at slow speed, mandrel 72 begins to rotate faster as the traverse similarly moves axially faster to maintain a constant ratio of mandrel revolutions to traverse motion. Mandrel 72 operates during the beginning of the winding cycle at a full rotational speed that decreases as the diameter of coil 50 increases so as to keep the linear speed of wire 18 constant. When the length of wire 18 on coil 50 approaches its pre-set maximum quantity, mandrel 72 begins to slow and then stops at the pre-set quantity. Mandrel 72 is rotated to a position where a first one of several channels 76 is positioned in line with banding wire 56 coming from banding wire supply 54. A length of banding wire 56 is moved to pass through channel 76 from a first to a second flange adjacent mandrel 72, through the bore of coil 50. The two ends of banding wire 56 are brought together by a pair of forks 74 a, 74 b (see FIGS. 2A-2D) and grasped by jaws 62 a, 62 b as forks 74 a, 74 b retract. Jaws 62 a, 62 b rotate to twist the ends of the banding wire together and clip the excess length therefrom. Jaws 62 a, 62 b open, and mandrel 72 rotates to the next sequential banding position, for example 90° farther, where the banding process is repeated. Cutter 46 cuts wire 18 between application of banding wires, and the cut end of wire 18 is turned back on itself and flattened by contact with bar 52 as mandrel 72 is rotated backwards for this purpose. In rotating to a next banding position, mandrel 72 causes each twisted wire end to pass under bar 52 to bend the twisted ends close to the periphery of coil 50. When a set of twisted ends is positioned appropriately, ram 66 is driven forward to flatten the twisted ends into a relatively safe placement against coil 50. After all banding is completed and the twisted ends are flattened into the surface of coil 50, flange 70 b moves away from mandrel 72 and a discharge ram is actuated to eject completed coil 50. Upon a signal from a sensor that coil 50 has moved out of the winding mechanism, flange 70 b, moves back into contact with mandrel 72 and the process is repeated.

[0027] While the present invention is described with respect to specific embodiments thereof, it is recognized that various modifications and variations may be made without departing from the scope and spirit of the invention, which is more clearly and precisely defined by reference to the claims appended hereto. 

What is claimed is:
 1. Apparatus for coil winding, comprising: (a) a supply of wire; (b) a winding station for forming the wire into a coil having a bore and an outer diameter; (c) means for driving the wire from the supply to the winding station; (d) a banding supply for supplying a length of banding material having a first end and a second end; (e) means for passing the first end of the length of banding material through the bore of the coil; and (f) means for securing the second end to the first end of the length of banding material so as to snugly band a portion of the coil.
 2. The apparatus for coil winding described in claim 1, wherein the winding station comprises a mandrel extending between a pair of flanges and the means for passing the first end of banding material through the bore of the coil comprises a banding material supply device and a channel formed in the flanges and the mandrel, the channel being inwardly open.
 3. The apparatus for coil winding described in claim 2, further comprising a bar positioned adjacent the winding station for orienting the secured first and second ends of the length of banding material close to a peripheral surface of the coil.
 4. The apparatus for coil winding described in claim 1, further comprising a ram operable for forcing a secured second end and first end of the banding material into contact with an outer diameter of the coil.
 5. The apparatus for coil winding described in claim 1, further comprising a sensor positioned adjacent the wire for detecting whether the wire is present.
 6. The apparatus for coil winding described in claim 1, further comprising a detector for detecting whether the wire is operating under excessive tension.
 7. Apparatus for coil winding, comprising: (a) a wire supply holder; (b) a winding station for forming a selected length of the wire into a coil having a bore and an outer diameter, the winding station comprising a pair of opposed flanges and a mandrel; (c) means for driving the wire from the wire supply holder to the winding station (d) a banding supply for supplying a length of banding material having a first end and a second end; (e) the flanges and mandrel being formed with a channel for passing the first end of the length of banding through the bore of the coil; and (f) a rotatable clamp for twisting the second end and the first end of the length of banding material so as to snugly band the coil.
 8. The apparatus for coil winding described in claim 7, wherein the channel in the flanges and mandrel is open in a direction facing the coil.
 9. The apparatus for coil winding described in claim 7, wherein the banding material is a wire.
 10. The apparatus for coil winding described in claim 7, further comprising a ram operable for forcing the twisted second end and first end into contact with an outer diameter of the coil.
 11. The apparatus for coil winding described in claim 7, further comprising a positionable guide mounted between the means for driving the wire and the winding station.
 12. The apparatus for coil winding described in claim 7, further comprising means for applying a controlled tension to the wire.
 13. The apparatus for coil winding described in claim 12, wherein the means for applying a controlled tension to the wire comprises a magnetic brake positioned for contacting the wire to apply tension thereto.
 14. The apparatus for coil winding described in claim 7, wherein the means for driving the wire comprises a drive capstan operable to drive the wire at a substantially constant linear speed.
 15. The apparatus for coil winding described in claim 7, further comprising means to drive the mandrel to apply tension to the wire.
 16. The apparatus for coil winding described in claim 15, wherein the mandrel is configured to receive and grip a starting end of the wire.
 17. A method for winding a wire to form a coil, comprising the steps of: (a) threading the wire along a path from a wire supply holder to a winding station; (b) attaching a starting end of the wire to a mandrel; (c) moving the length of wire along the path at a substantially constant linear speed; (d) causing the mandrel to rotate; (e) causing the wire to move in an axial direction relative to the mandrel at a selected traversing speed; (f) stopping the rotation and traversing at the completion of winding a pre-determined length of wire to form a coil; (g) banding the coil of wire in a plurality of places; and (h) ejecting the banded coil.
 18. The method for winding a wire as described in claim 17, wherein the step of banding the coil of wire comprises passing a first end of a length of banding material through a bore of the coil and securing a second end to the first end.
 19. The method for winding a wire as described in claim 17, wherein the step of banding the coil of wire comprises passing a first end of a length of banding material through a channel formed in the mandrel and securing a second end to the first end.
 20. The method for winding a wire as described in claim 17, further comprising cutting an end of the wire and bending the end of wire back to maintain the coil as wound.
 21. The method for winding a wire as described in claim 17, wherein the step of causing the mandrel to rotate comprises varying the mandrel rotating speed so as to match the rotation of the mandrel to the substantially constant linear speed of movement of the length of wire.
 22. The method for winding a wire as described in claim 17, wherein the step of causing the mandrel to rotate further comprises causing the mandrel to rotate slowly for a selected number of revolutions and thereafter to rotate more quickly.
 23. The method for winding a wire as described in claim 22, further comprising causing the mandrel to rotate slowly during a period when a quantity of wire on the mandrel approaches the pre-determined length of wire and thereafter to stop.
 24. The method for winding a wire as described in claim 17, wherein the step of banding the coil of wire in a plurality of places comprises banding the coil of wire in four places.
 25. The method for winding a wire as described in claim 17, wherein the step of causing the wire to move in an axial direction relative to the mandrel further comprises adjusting the speed of the relative movement in the axial direction in relation to the rotation of the mandrel.
 26. The method for winding a wire as described in claim 18, wherein the step of securing comprises twisting the first and second ends together and the method further comprises causing the twisted ends into close contact with a peripheral surface of the coil.
 27. The method for winding a wire as described in claim 26, wherein the step of causing the twisted ends into close contact with a peripheral surface of the coil comprises impacting the twisted ends with a ram. 